Umhlahlandlela wokusebenzisa ukujoyina kwangaphakathi ku-SQL ku-Group Data kusuka kumathebula amaningi

Sebenzisa ukujoyina kwangaphakathi kwe-SQL ukuhlanganisa idatha kusuka kumatafula amathathu noma ngaphezulu

Ungasebenzisa izitatimende ze-SQL JOIN ukuze uhlanganise idatha kusuka kumatafula amathathu noma ngaphezulu. I-SQL JOIN iguquguquka kakhulu, futhi ukusebenza kwayo okunamandla kungasetshenziswa ukuhlanganisa idatha kusuka kumatafula amaningi. Ake sibuke izitatimende ze-SQL ezikuvumela ukuba uhlanganise imiphumela emathebula amathathu ahlukene usebenzisa ukujoyina kwangaphakathi.

Isibonelo sokujoyina kwangaphakathi

Isibonelo, thatha amatafula afaka abashayeli etafuleni elilodwa kanye nemoto yokufanisa kwezemoto okwesibili. Ukujoyina kwangaphakathi kwenzeka lapho kokubili imoto nomshayeli bekhona edolobheni elifanayo. Ukujoyina kwangaphakathi kukhetha yonke imigqa kusuka kokubili amatafula afana nomdlalo phakathi kwamakholomu wendawo.

Isitatimende se-SQL ngezansi sihlanganisa idatha kusuka kumatafula Amashayeli Nezimoto lapho kwenzeka khona umshayeli nemoto edolobheni elifanayo:

HLOLA igama lokugcina, igama lokuqala, umaki KUSUKA abashayeli, izimoto NOMA lapho abashayeli.wahlukaniswa = izimoto

Lo mbuzo uveza imiphumela elandelayo:

Igama lokuqala igama lami -------- --------- --- Baker Roland H122JM Smythe Michael D824HA Smythe Michael P091YF Jacobs Abraham J291QR Jacobs Abraham L990MT

Manje, wandisa lesi sibonelo ukufaka itafula lesithathu. Cabanga ukuthi ufuna ukufaka kuphela abashayeli kanye nezimoto ezikhona ezindaweni ezivuliwe ngempelasonto. Ungaletha ithebula lesithathu embuzweni wakho ngokukhulisa isitatimende se-JOIN kanje:

Khetha igama lokugcina, igama lokuqala, ithegi, evulekile_ukuphuma kwe-FROM FROM abashayeli, izimoto, izindawo LAPHO abashayeli.location = izimoto.wahlukaniswa kanye nezimoto.location = izindawo.wahlukaniswa kanye nezindawo.open_weekends = 'Yebo' igama lokugcina igama lombuzo ovuliwe_i-imeyli -------- ---------- --- ------------- Baker Roland H122JM yebo Jacobs Abraham J291QR yebo Jacobs Abraham L990MT yebo

Lesi sandiso esinamandla kwisitatimende esiyisisekelo se-SQL JOIN ikuvumela ukuba uhlanganise idatha ngendlela eyinkimbinkimbi. Ngaphandle kokuhlanganisa amathebula onokujoyina kwangaphakathi, ungasebenzisa le nqubo ukuhlanganisa amatafula amaningi usebenzisa ukujoyina kwangaphandle. Amajoyini angaphandle ahlanganisa imiphumela ekhona etafuleni elilodwa kodwa ayinayo umdlalo ohambelana netafula elihlanganisiwe.